The invention relates generally to medical devices and procedures, including, for example, medical devices and methods for storing and injecting a corneal tissue graft.
Corneal transplantation is a widely practiced ophthalmic surgical procedure where the cornea from a donor is used to replace a scarred or diseased cornea of a patient to restore vision. Such corneal implants are performed to treat a variety of blinding diseases. Some of the most common corneal conditions that necessitate corneal transplantation include: Corneal Edema, Corneal Dystrophies, Keratoconus, and other conditions that lead to corneal scarring. Many corneal transplants are necessitated by corneal edema. Corneal edema, or swelling, can sometimes occur after cataract surgery or due to diseases such as Fuchs' dystrophy (i.e., an accumulation of focal excrescences called guttae and thickening of Descement's membrane, leading to corneal edema and loss of vision). Left untreated, the corneal swelling can cause blurred or foggy vision and can advance to a point such that tiny blisters form on the surface of the cornea. This condition results due to disease of the corneal endothelium, which is a single monolayer of specialized cells that line the back of the cornea.
Until recently, the management of corneal edema secondary to diseased corneal endothelium was with a penetrating keratoplasty (PK) procedure. A PK procedure is a surgical procedure where a full thickness corneal button replaces a full thickness button of the patient's cornea. Specifically, all of the layers of the cornea are replaced. In a PK procedure the donor cornea is sutured into the patient's cornea using nylon sutures. While penetrating keratoplasty has been very successful in restoring a clear cornea and eliminating the symptoms of corneal edema, due to wound healing irregularities, as well as difficulty creating a donor corneal button that is the exact size of the recipient's corneal button, high degrees of corneal astigmatism frequently results. This can lead to a situation where the patient has a clear cornea, but is unable to see through it because of optical aberrations.
Another known procedure is referred to as endothelial keratoplasty, which differs from penetrating keratoplasty in that only the posterior layers of the cornea are transplanted to the donor eye. Although endothelial keratoplasty has grown more popular as a treatment of corneal edema caused by endothelial cell failure, there are known problems associated with endothelial keratoplasty. One known problem is the potential damage to the donor corneal epithelium caused by current techniques of folding the tissue and then pushing the folded tissue through the corneal wound using forceps. This procedure can cause a crush injury to the delicate endothelial cells of the donor transplant tissue. Additionally, to fold the donor tissue into the eye using known techniques, a relatively large incision (e.g., 6 mm) is typically necessary. The large incision must be sutured closed before the endothelial keratoplasty button (e.g. tissue graft) is unfolded, which may lead to endothelial cell loss.
One known technique for endothelial keratoplasty is referred to as deep lamellar endothelial keratoplasty (DLEK). In this technique a pocket is made within the cornea and diseased corneal endothelium is excised along with a layer of corneal stroma. Healthy lamellar corneal stromal endothelial tissue is then transplanted into the space left by the excised diseased tissue. Another known technique is called Descemet's stripping endothelial keratoplasty (DSEK) or Descemet's stripping automated endothelial keratoplasty (DSAEK). In this technique, a lamellar corneal stromal endothelial transplant graft is transplanted into an anterior chamber of a patient's eye. For example, a diseased corneal endothelium in a recipient's eye is stripped away with surgical instruments and then the lamellar corneal stromal endothelial transplant graft is inserted into the anterior chamber through a full thickness corneal incision. The graft can then be held in place against the stripped posterior corneal stromal surface by, for example, an air bubble until the graft is able to heal in position. In some cases, a suture or sutures can be used to secure the tissue graft placement.
In both DLEK and DSEK (and DSAEK), it would be advantageous to be able to insert a relatively large transplant atraumatically through a small corneal or scleral incision. A larger transplant has more corneal endothelial cells and should produce better results in the treatment of corneal endothelial diseases. As discussed above, in some known methods, however, the tissue graft is folded and/or is grasped with forceps, which can damage the tissue cells. Moreover, the transplant is typically severely compressed as it passes through the corneal incision. In such procedures, the delicate corneal endothelial cells of a transplant can be damaged or killed during the insertion process.
Corneal implants can be made of either synthetic materials (e.g. prostheses) or can be biological in origin (e.g. donor grafts). Like corneal transplant grafts for DSEK or DLEK, synthetic corneal implants (e.g. corneal inlay prostheses) are also very delicate. In many cases, these corneal inlays may be as thin as 30 to 40 microns, which makes them very easily torn by forceps. Thus, there is also a need for an improved method to place corneal inlays atraumatically through a small incision.
There are many different types of corneal implants that have been developed for the treatment of refractive error and disease. Because of limitations in the methods of creating corneal pockets, these implants have all been designed for placement in the cornea by creation of a corneal incision, which is either similar in size to the smallest dimension of the implant or larger. Recently, two methods of corneal pocket creation have been devised which can create a pocket with an external opening width that is less than the maximum internal width of the pocket. These two methods are pocket creation by the femtosecond laser and, of particular interest, cornea cutting, as described in US 2004/0243159 and 2004/0243160 the full disclosure of which is incorporated herein by reference.
One known delivery system used in DSAEK is the Moria Busin device, which is a glide spatula for the insertion of a donor lamellar button. It provides a “pull-through” technique and minimizes intraoperative manipulation of the graft and the possibility of endothelial cell loss, but still requires the surgeon to load the tissue graft. There are 5 steps in the Busin “pull-through” technique: (1) The Busin glide is loaded with the donor lamella, endothelial side up; (2) The donor lamella is then pulled into the glide opening; (3) The glide is then inverted and positioned at the entrance of a nasal clear-corneal tunnel. A forceps passes through a temoral paracentesis wound across the anterior chamber and grasps the donor lamella from the glide. An anterior chamber maintainer is placed at 12 o'clock position to reform the anterior chamber; (4) The donor lamella is pulled into the anterior chamber; and (5) The donor lamella is left to unfold spontaneously under continuous irrigation.
There are also known delivery systems for placement of intraocular lenses (IOLs) into the posterior chamber of a patient's eye through a small incision. Such delivery systems, however, are designed for small incision cataract surgery and are typically not well adapted for use as a delivery system for corneal implants through a small incision. For example, a typical intraocular lens implant may be 1 mm or greater in thickness, whereas the typical corneal transplant for DLEK or DSEK is between 0.1 to 0.15 mm in thickness. Moreover, as noted above, the thickness of a corneal inlay prosthesis may be as little as 30 to 40 microns. In addition, the size and shape of an IOL is typically different from that of a corneal transplant. An IOL is typically 12 mm to 13 mm in length and 5 mm to 6 mm wide, whereas a corneal transplant is typically circular in shape and has a diameter, for example, of 8 mm to 9 mm. In the case of a corneal prosthesis inlay, the diameter may range from 1 mm to 10 mm. Finally, IOL delivery systems are designed to greatly compress the IOL during the insertion process, which can either damage or destroy a living corneal transplant.
Intraocular lenses for cataract surgery have also been designed to be placed through a small incision, however, these small incision cataract surgery lenses cannot practically be used within a corneal pocket. Most small incision cataract surgery lens implants are typically too thick to be placed within a corneal pocket. For example the typical thickness of a cataract surgery lens implant is 1 mm or more, which is substantially thicker than the human cornea, which is usually between 0.5 mm to 0.6 mm. Some corneal implants that have been designed only have a thickness of about 0.05 mm. Moreover, the cataract surgery lens implants have haptics, which are extensions from the lens implant designed to keep the lens implant fixated within the capsular bag. Haptics are not present, and not necessary, for corneal implants. Finally, the cataract surgery lens implants are not designed to be biocompatible with the cornea and would not be tolerated as corneal implants. Thus, the delivery systems designed for small incision cataract surgery lens implants are not well adapted for use as a delivery system for small incision corneal implants.
Thus, a need exists for an apparatus and method for storing a corneal tissue graft in a pre-cut ready to use state for transport to a surgeon that allows the tissue graft to remain untouched by the medical practitioner upon receipt of the tissue graft and during the implantation procedure. There is also a need for an apparatus and method for corneal implantation that does not damage or destroy a living corneal tissue graft during storage, transport and the implantation process, while providing ease of transplant for the surgeon.